Most natural flyers and man-made flying objects are having only one pair of symmetric wings for lift production that are attached to a centrally positioned body. The exceptions to this configuration are related to very rare smaller natural flyers with two pairs of flapping wings and flying objects with multiple smaller rotary wings such as helicopters that have insufficient lift capacity, speed, and range for the current mass-transportation needs.
The following configurations of aircraft for mass transportation have been created so far:                “Tube-and-wing” aircraft configuration with a pair of wings for lift production and roll control, fuselage for payload accommodation, and empennage for pitch and yaw control.        “Tube-and-wing” configuration with only a vertical tail where wings except for lift production are used for flight control in pitch and roll directions while vertical tail for yaw control.        “Canarded tube-and-wing” configuration where canards are substituting tailplane for pitch control.        “Tailless flying wing” configuration where a single wing is used for lift production, payload accommodation, and flight control.        “Tailed flying wing” configuration where tail surfaces are assisting a single wing in pitch and yaw flight control.        “Canarded flying wing” configuration where canards are substituting the role of tailplane in pitch direction.        Multiple wing configuration with more than one wing arranged in flight direction for simultaneous lift production and flight control.        
The first idea of an aircraft having more than one fixed wing appeared more than 80 years ago in U.S. Pat. No. 2,147,968 of Feb. 21, 1939. This patent suggested a substitution of empennage used only for flight control with a fixed rear wing that in addition to flight control is capable to assist with lift production in order to increase the lift capacity of aircraft. This idea has been very attractive, thus initiating many subsequent patents since then with different solutions for multiple wing arrangements. However, over the past 80 years, nobody has been able to develop a realistic aircraft that is competitive with the current prevailing tube-and-swing configuration with a single wing and empennage for mass transportation as multiple wing idea requires more complex flight mechanics relative to the single wing arrangement with separate surfaces for lift production and pitch control.
The initial U.S. Pat. No. 2,147,968 whose idea is similar in some ways to double wing aircraft as outlined in this application did not offer any specifics relative to the wing geometry, size, and gravity center position relative to the wings, as well as any other aerodynamic feature of the wings that would address how to achieve lift production on both wings and simultaneously a sufficient level of flight control and safety of such aircraft.
The only specific in the initial patent was outlined in claim 1 as “a rear wing staggered relative to the forward wing by a distance at least equal to the width of the front wing” with no specifics as to in which direction “distance” is referred to whether being horizontal, vertical, diagonal, etc., which is important for flight mechanics. The confusion in this regard is further increased with a reference in specification “it is to be noted that the number and relative position of the front and rear wing may be varied”, which relates to a modification shown in FIG. 8 that reflects an additional vertically coupled front wing with a rear wing.
From the standpoint of shape and size of front and rear wing, only one generic sentence was noted in specification where it says that “the maneuvering may be insured by means of hinged ailerons mounted on wings 1 and 2 of which the shapes and dimensions, as will be understood, are selected in such manner to ensure the desired lift and stability.” The position of gravity center relative to front and rear wing that is essential for flight mechanics of a double wing configuration was completely omitted in claims, specification, and drawings.
The “double wing aircraft” idea of this patent application contrary to the above initial patent is revealing geometric configuration variables related to the mutual size and distance between front and rear wing, their aspect ratio that is affecting the wing shapes, and aerodynamic features of both wings as reflected with the position of their air pressure centers relative to the position of gravity center in flight direction that are forcing rear wing to generate a substantial positive lift and high stability of aircraft in stationary flight conditions by using the best simultaneous combinations of suggested variables. The suggested shape of wings as the consequence of low aspect ratio is resulting with longer chords and lower airfoil thickness, which along with low lift coefficient due to the large size of both wings is reducing aerodynamic drag.
The double wing aircraft idea relative to the initial U.S. Pat. No. 2,147,968 on the top of the above specific suggested variables is additionally offering many innovating ideas related to the specific architectural solutions for connecting front and rear wing, specific solutions for payload accommodation, as well as specific accommodation and connections of engines and landing gears to the airframe.
All patents related to aircraft that are having more than one wing based on the initial U.S. Pat. No. 2,147,968 until today may be sorted in two general groups:                Pure double wing aircraft without any other planar airlifting surfaces        Multiple wing configurations with more than two planar airlifting surfaces        
An efficient aircraft configuration with two or more wings should generate approximately the same lift coefficient in cruise on all wings from the standpoint of aerodynamic efficiency while guaranteeing sufficient flight controls from the standpoint of flight safety where the term “wing” refers to an airlifting surface that is providing a positive lift in stationary flight.
In order to provide for a stable stationary flight, multiple wing aircraft must have at least two wings, one in front of gravity center and other behind gravity center with both wings producing positive lift in order to provide for the static stability in stationary flight and sufficient flight control in all flight regimes. An aircraft with more than two planar surfaces from the standpoint of both aerodynamic and flight control efficiency is aerodynamically oversized.
If there is not enough lift in stationary flight, it is more rational to increase the size of the existing wings as opposed to adding another wing. If there is insufficient level of flight control, it is more rational to adjust the mutual size and distance of existing two wings relative to gravity center than add new flight control surfaces. For this reason, the patents with more than two airlifting surfaces will not be addressed further.
Aircraft configurations with only front and rear wing may be sorted in three groups formed by:                Transformation of stabilizing tailplane set behind gravity center into a rear wing and simultaneously shifting the same forward towards gravity center while increasing its size.        Transformation of destabilizing canard set in front of gravity center into a front wing by shifting the same in aft direction towards the gravity center and increasing its size.        Formation of a substantial tandem wing configuration with gravity center between and far away from both front and rear wing.        
The initial U.S. Pat. No. 2,147,968 and double wing aircraft of this patent application fall in the first group with a larger main front wing. Other than shifting a smaller tailplane surface forward towards gravity center while increasing its size, it is necessary to additionally shift the front wing airlifting forces in front of gravity center in stationary flight by either shifting the gravity center in aft direction behind front wing lifting forces or shifting the front wing air pressure center forward away from the gravity center, or doing both simultaneously. During this transformation, the rear wing lifting forces are staying substantially behind gravity center with its trailing edge flight control surfaces far behind the gravity center in order to guarantee a sufficient level of pitch control.
The double wing aircraft that belong to the second group as in U.S. Pat. Nos. 4,030,688 and 8,123,16062 are formed from a low-stable canarded aircraft that have a large main rear wing whose airlifting forces are positioned close to gravity center. An added small canard that is positioned moderately in front of gravity center is assisting with static pitch stability in stationary flight while additionally providing for pitch control in all flight regimes. The canard size of such aircraft is usually much smaller than the tailplane size to prevent a higher aircraft natural destabilization with larger destabilizing canard surfaces that are positioned in front of gravity center.
The transformation of canarded aircraft into a double wing configuration with a front canarded wing starts with the shift of aircraft gravity center forward away from rear wing air pressure center towards the canard, while simultaneously shifting the canard in aft direction towards the shifted gravity center with the increase of canard size to provide for a static stability of aircraft with higher positive lift production by the forward positioned canarded wing. This solution with canarded front wing and the large main rear wing has greater limitations during transformation when compared to the first group with tailplane as the forward shift of gravity center and aft shift of canards are shifting trailing edge flight control surfaces of the canard very close to the gravity center, thus making the canard inefficient for commanded pitch control when the forward shift of gravity center is making the large rear wing more aerodynamically sluggish for commanded pitch control of the aircraft, whereby decreasing the commanded pitch control efficiency and making such aircraft unsuitable for commercial transportation.
The third solution with a substantial tandem wing arrangement as in U.S. Pat. No. 4,390,150 is characterized with a long distance between front and rear wing, while the gravity center being positioned far between both wings. In this arrangement, a large front wing set far in front of gravity center is acting as a highly destabilizing canard, hence such aircraft are naturally either low-stable or unstable, thus such arrangement is also not suitable for commercial transportation.
The U.S. Pat. No. 8,056,852 of Nov. 15, 2011 called “Longitudinal Flying Wing Aircraft” reflects a multiple wing configuration with a large front wing that is adjusted for payload accommodation and gravity center positioned therein. The front wing carries a rear vertical reinforcement to which a “V” tail is connected to as rear stabilizing surfaces. “V” tail stabilizing surfaces on their upper ends carry integral rear airlifting surface with engine aerodynamic cover integrated in between. “V” tail with its high sweepback angle is connected to the aft portion of the vertical reinforcement of front wing to increase its own stabilizing function and simultaneously shift rear stabilizing airlifting surface in aft direction to the highest extent possible, whereby altogether shifting the aircraft neutral point and gravity center with positive static margin behind front wing lifting forces in order to enable rear airlifting surfaces to generate positive lift in cruise. However, far aft position of rear airlifting surfaces behind gravity center is increasing its stabilizing role but decreasing their ability to generate higher positive lift in cruise.